The present invention relates to mobile RF terminals required to conduct bi-directional communications with a base station via a satellite link, and more particularly to a method and apparatus for identifying which one of a plurality of mobile terminals is causing interference with one or more satellites adjacent a target satellite through the use of a binary search scheme.
With mobile RF terminals located on mobile platforms such as aircraft, cruise ships and other moving platforms, communicating with a ground station via a transponded satellite, there is always the remote possibility, in spite of the safeguards that may be built into the mobile terminal, that the terminal may fail in an unanticipated manner. In such event, there is the possibility that the mobile terminal may cause interference with other satellites orbiting in the geo arc adjacent to the target satellite with which the mobile terminal is communicating.
It is also recognized that Fixed Services Satellite (FSS) operators may have difficulty in locating interference from VSAT (Very Small Aperture Terminal) systems that consist of thousands of unsophisticated terminals at remote sites.
Therefore, there exists a need for a ground station in communication with a plurality of mobile terminals via a transponded target satellite to be able to quickly identify a malfunctioning mobile terminal which is causing interference with non-target satellites from among a plurality of mobile terminals accessing the target satellite and to quickly resolve the interference incident.
The present invention is directed to a system and method for identifying an interfering mobile RF terminal from one of a plurality of mobile RF terminals. The method involves using a base station, such as a ground station having a network operations center (NOC), to analyze signals transmitted by the mobile terminals to the ground station via a transponded target satellite.
A binary search scheme is employed to quickly check designated groups of mobile terminals to determine if the interfering signal is being caused by one of the terminals in a group. The plurality of mobile terminals accessing the target satellite is first divided in a subplurality of two groups. The NOC then commands one of the subpluralities to stop transmitting momentarily to determine if the interference has abated. If not, the NOC performs the same operation with the other subpluralities to determine which subplurality of mobile terminals is causing the interference. Once that group (i.e., subplurality) is identified, the NOC again divides the mobile terminals of that subplurality into two further subpluralities. One of these two subpluralities of mobile terminals are then commanded to stop transmitting momentarily so that the NOC can identify if the interference has abated. This process is repeated using successively smaller and smaller subpluralities of mobile terminals until the NOC identifies the specific mobile terminal that is causing the interference. It will be appreciated that this process is preferably carried out by the NOC communicating with the operator of the non-target satellite so that the NOC can quickly verify if the subplurality of mobile terminals being checked includes the interfering terminal. Once the interfering mobile terminal is identified, it can be commanded by the NOC to shut down or to reduce its data transmission rate (thus effectively reducing the power level of its transmitted signals) to eliminate the interference with the non-target satellite.
The above-described method can be used to check a single mobile terminal for interference within a time span of about 5-10 seconds. A transponded satellite accommodating 20-30 aircraft can be checked typically in less than 5 minutes.